In physics, resonance is the tendency of a system to oscillate with high amplitude when excited by energy at a certain frequency. This frequency is known as the system's natural frequency of vibration or resonant frequency. A resonant object, whether mechanical, acoustic, or electrical, will probably have more than one resonant frequency (especially harmonics of the strongest resonance). It will be easy to vibrate at those frequencies, and more difficult to vibrate at other frequencies. The resonant object will “pick out” its resonant frequency from a complex excitation, such as an impulse or a wideband noise excitation. In effect, it is filtering out all frequencies other than its resonance. Mechanical resonance is the tendency of a mechanical system to absorb more energy when the frequency of its oscillations matches the system's natural frequency of vibration (its resonant frequency) than it does at other frequencies.
When playing a musical instrument, such as a violoncello (commonly referred to as the cello), the cellist will choose which string or strings to play by depressing the string or strings on a fingerboard while bowing in techniques such as standard bowing, double stops, col legno, spiccato or staccato or by plucking using pizzicato. A difficulty that arises when performing using these various playing techniques on the cello is that during play, mechanical resonance may occur in strings and/or the body of the instrument. Such mechanical resonance causes undesired sound waves hereinafter referred to as wolf tone which may be detrimental to the sound during the performance of the cellist.
In addition, resonance may be detrimental in other acoustic, mechanical or electrical devices.